1. Field of the Invention
This invention relates to a mouthpiece for a semi-closed type of breathing apparatus in which carbon dioxide is removed from breathing air circulating in a breathing circuit, breathing air is supplied into the breathing circuit, and surplus breathing air is discharged to the outside.
2. Description of Related Art
In general, this semi-closed type of breathing apparatus is equipped with a mouthpiece, a carbon dioxide absorber (canister) for absorbing carbon dioxide and a breathing gas bomb (an air tank). In the semi-closed type of breathing apparatus thus constructed, carbon dioxide is removed from breathing air (gas) circulating in the breathing circuit by the canister, and the breathing air is supplied from the air tank into the breathing circuit while surplus breathing air is discharged from the breathing circuit.
As a conventional breathing apparatus has been well known one as disclosed in Japanese Laid-open Utility Mode Application No. 1-134598. The mouthpiece of the breathing apparatus as disclosed in this publication has a breathing chamber in a case thereof, and the breathing chamber is formed with an air inhaling port and an air exhaling port. A check valve which is opened through an air inhaling operation is provided at the inhaling port, and the air inhaling port is opened or closed by the operation of the check valve.
On the other hand, a slide member is provided at the air exhaling port side, and the air exhaling port is opened or closed by the movement of the slide member in the breathing operation. If water intrudes into the breathing chamber, the slide member is moved by a hand to intercommunicate a drain port formed in the case with the breathing chamber, and the water which has intruded into the breathing chamber through the drain port is blown out while closing the drain port in the air exhaling operation.
In the conventional semi-closed type of breathing apparatus as described above, the slide member also serves as an exhaling valve, and thus the apparatus is so designed that the exhaling port is closed through the movement of the slide member. Accordingly, when water intrudes through a breathing port of the mouthpiece, there occurs an unfavorable case where water is liable to intrude into the breathing circuit through the opened exhaling port. The intrusion of water into the breathing circuit causes the function of the carbon dioxide absorber to be damaged. Further, in the semi-closed type of breathing apparatus, a check valve is provided at each of the air exhaling port and the air inhaling port. The air inhaling port is ordinarily closed, and it is opened only in the air exhaling operation. In this valve structure, the air exhaling port may be opened by the weight of water itself, so that the intrusion of water cannot be prevented.